Multistage pump balancing means



Oct. 23, 1934. w H. NOB-LE MULTISTAGE PUMP BALANCING MEANS Filed March 21, 1931 H v, l- R V 5 m M 0 T & N A m 4/ M. a Q Q Wu 7 I 1 I I H I 4 h C E 3 k -iwmn D IN n V W? H Id HUI v 63 Q m m M\ w\ Patented Oct. 23, 1934 UNITED STATES MULTISTAGE PUMP BALANCING MEANS William H. Noble, Easton, Pa., assignor to Pennsylvania Pump & Compressor Company, Easton, Pa., a corporation of Pennsylvania Application'March 21, 1931, Serial No. 524,355

11 Claims.

This invention relates to means for balancing multi-stage centrifugal pumps and in particular to a method for balancing centrifugal pumps having an odd number of impellers.

An object of the invention is to provide a balancing means applicable generally to centrifugal pumps but more particularly adapted for muti-stage single intake impeller .pumps having one group of impellers opposed to another group, the number of impellers in the groups being unequal. I

It is well-known that in multi-stage pumps of the centrifugal type in which the impellers have single'intakes, complete balancing may be effected by arranging the impellers so that the.

axial thrust of half of the impellers will balance the axial thrust of the remaining impellers. For this purpose half of the impellers are opposed to the other half. In pumps having an even number of impellers this disposition of the impellers effects the balancing and no special balancing means is required. Certain installations, however, require an odd number of impellers which prevent complete balancing in the above manner. The impellers, however, are arranged in two groups so that some will oppose the others, one impeller only therefore being unbalanced.

A primary object of the invention is therefore to provide simple and effective means to balance an odd impeller of a multiple impeller centrifugal pump.

More specifically it is an object ofthe invention to provide means varying the areas of the impellers exposed to unbalanced pressures so that the total thrust of one group of impellers in one direction will equal the thrust in the opposite direction of the opposed group of impellers.

And finally it is an object of the invention to vary the diameter of the rotor at that portion between adjacent opposed impellers where the rotor shaft passes through one of the diaphragms of the casing.

In the present system selected to illustrate the invention a pump having five single intake impellers is shown, two having intakes upon the left-hand side and three having intakes upon the right-hand side. It will therefore be seen that unless some means is provided for balancing the end thrust of the odd impeller the impeller shaft will be forced toward the right, as viewed in the figure, by the unbalanced impeller. I am enabled to balance this odd impeller by simple means by enlarging that portion of the rotor where it passes through one of the diaphragms of the pump casing, this enlarged diameter of the rotor being calculated in a manner presently to be described, the position of the enlarged bearing being between two adjacent impellers of opposite hand. This present invention does not contemplate balancing end thrusts occasioned by friction of flow of the fluid through passages of the casing. These unbalanced forces are usually of minor importance and if balancing is necessary may be effected in any desired manner.

With the above and other objects in view my invention includes the features of construction and operation set. forth in the following specification and illustrated in the accompanying drawing.

In the accompanying drawing annexed hereto and forming a part of this specification, I have shown my invention in a five stage centrifugal pump but it will be understood that the invention can be otherwise embodied and that the drawing is not to be construed as defining or limiting the scope of the invention, the claims appended to this specification being relied upon for that purpose.

In the drawing the figure is a longitudinal view in section of a com lete pump showing the present invention applied thereto parts being omitted which are unrelated to this invention.

In the above mentioned drawing I have shown but one embodiment of the invention which is now deemed preferable, but it is to be understood that changes and modifications may be made within the scope of the appended claims without departing from the spirit of the invention.

Briefly, and in its preferred aspect, my invention may include the following principal parts: First, a pump casing having impeller cavities separated by casing diaphragms; second, a rotor within said casing having an odd number of impellers disposed in opposed relation; third, conduits within said casing for the passage of liquid through said impellers in succession; and fourth, bearings upon said diaphragms rotatably fitting said rotor between each of said impellers, one or more of said bearings being enlarged to vary the area of the impellers exposed to unbalanced pressures.

Referring more in detail to the figure of the drawing, I provide a pump unit having a lower casing member 10 and an upper casing member 11 suitably secured together in the usual or any preferred manner. These two members 10 and 11 of the casing provide a plurality of spaced cavities, one for each of the individual impellers 12 separated by diaphragms 13 which have portions 13- closely engaging the rotor shaft 14 or parts of the impellers 12.

The pump intake 15 is shown at the left-hand end of the casing and the course of the water through the casing is first to impeller R1, thence to impeller R2. From impeller R2 the liquid is conveyed within an opening or conduit 16 formed within the lower casing member 10 to the opposite end of the casing, whereupon it enters and passes through impeller R3. From impeller R3 the liquid passes to impeller R4 and then finally to impeller. R5. From impeller R5 the liquid is discharged into the final discharge conduit 17.

It will be seen that the effect of the intake pressure of impellers R1 and R2, having their intake upon the left-hand'side, will force the rotortoward the left. Impellers R3, R4, and R5, for a similar reason, will force the rotor toward the right of the figure. As but two thrust in one direction and three in the other direction, and all are of equal size and have equal pressure, it will be\seen that there is a resultant thrust of the complete rotating unit equal to that of one impeller toward the right. This requires some means of balancing for satisfactory operation of the pump, and is accomplished by the provision of an enlarged spacer 18 disposed upon the rotor between impellers R2 and R5. This spacer 18 rotatably engages one of the diaphragm bearing members 13. I

As a concrete example let it be assumed that the pump is arranged for discharging water at 500 pounds pressure, the water at its intake being 0. There will then be 100 pounds pressure increment effected by each impeller. For convenience also we may assume the outside diameter D of the impeller suctions as equal to 5 inches or as having approximately 20 square inches area. D,

the diameter of the rotor upon the inner diameter of the suctions, may be equal to two and one-half inches or having approximately five square inches area. The diameter of the spacer 18 between the adjacent opposed impellers is unknown and will be indicated by D.

With the above information we can equate the thrust of the unbalanced areas of each of the impellers toward the right with the thrust-to- M ward the left and then solve for the diameter D In this equation thrust toward the right will be indicated by and the thrust toward the left by The summation of these thrusts for a balanced pump should be zero. In this equation AD, AD and AD represent the areas of the rotor at the points marked D' D and D respectively.

From the above it will be seen that by enlarging the diameter of the rotating part slightly between adjacent opposed impellers complete balancing of the pump is obtained. From an inspection of the above equation also it will be seen that regardless of the discharge pressure any pump having similar impellers, if balanced for one discharge pressure, the pump will be balanced for all discharge pressures. This is, of course, assuming that the pressure increment at each impeller is equal. Furthermore, leakage through the hear-- ing will have no effect upon the completeness of the balancing so that continued wear of the pump will not effect any unbalancing.

I have indicated the member 18, the diameter of which is calculated as above described, as a separate member fitting over the shaft 14 and holding the impellers R2 and R5 properly spaced apart. It will be obvious, however, that the member 18 does not necessarily have to be a separate member nor be usable as a spacer for the impellers. The member 18 is so made in order to adapt the construction required for the present invention to present forms of pumps.

What I claim is:

1. A muIti-stage centrifugal pump comprising in combination, a casing having diaphragms dividing said easing into separated cavities, impellers within said cavities disposed in opposed relation to each other, a shaft extending through said casing for supporting and rotating said impellers, and spacing means on said shaft between said impellers rotatably engaging the casing, the diameters thereof being varied to effect balancing of said impellers.

2. A multi-stagecentrifugal pump comprising in combination, a casing having diaphragms dividing said casing into separated cavities, impellers within said cavities disposed in opposed relation to each other, a shaft extending through said casing for supporting and rotating said impellers, and spacing means on said shaft between each of said impellers rotatably engaging the casing, the diameter of the spacing means between two adjacent impellers of opposite hand having a greater diameter than the others to effect balancing of said impellers.

3. In a multi-stage centrifugal pump having an odd number of impellers of single suction type mounted upon a common shaft, all but one impeller being arranged in pairs in opposed relation and the odd impeller being adjacent an impeller of opposite hand, diaphragms within said casing separating said impellers, and a spacing member between the odd impeller and its adjacent impeller, said member rotating with said shaft and rotatably engaging one of said diaphragms, the diameter of said member being increased as compared to the diameters of the rotating parts engaging the remaining diaphragms to reduce the area of said odd impeller acted on by the discharge pressure against the side opposite its suction. I

4. A centrifugal pump comprising in combination, a casing having a plurality of diaphragms dividing the casing into an odd number of cavities, impellers within said cavities mounted upon a common shaft, means to rotate said shaft and impellers, fluid conduits within said casing connecting said cavitiesso that some of said impellers will be in opposed relation to others, and spacing members between adjacent impellers and bearing upon said casing, the diameter of the spacing member between two adjacent impellers of opposite hand having a diameter greater than the diameter of the remaining spacing means so 1,978,277 that said larger diameter spacing member will the areas of the others of said running fits so that e forces acting thereupon will produce a resultant force opposite in direction and f amagnitude substantially equal to the total unbalanced forces acting upon the other portions of said shaft and impellers.

6. The method of counterbalancing end thrust of the rotative structure in afmulti-stage centrifugal pump having single suction impellers disposed in opposed relation to each other, which consists in proportioning the transverse crosssectional areas of those sections of the rotative structure positioned between the groups of oppositely disposed single-suction impellers in Such ratio that the forces acting thereupon will be sufficient to substantially counterbalance the cumulative unbalanced forces acting upon the other portions of said rotative structure.

7. The method of counterbalancing end thrust of the rotative structure within the casing of a multi-stage centrifugal pump having single suctionimpellers disposed in opposed relation to each other, which consists in proportioning the transverse cross-sectional areas of those sections of the rotative structure engaging said casing and positioned between the groups of oppositely disposed single suction type impellers in' such ratio that the forces acting thereupon produce a resultant force opposite in direction but of a magnitude substantially equal to the cumulative forces acting upon the other portions of said rotative structure;

8. A multi-stage .centrifu gal'pump including a casing, a shaft rotatably mounted therein,

groups of single-suction type impellers mounted in opposed relation upon said shaftand each impeller being adapted to form a close running fit with said casing, fluid passages serially connecting said impellers and arranged whereby the firstand third-stage impellers are adjacent opposite ends of said casing, and means for balancing the end t of said impellers and shaft by proportioning the area of the fit between the casing and the backs of adjacent opposed impellers sufiiciently different from the areas of the others of saidrunning fit s between the casing and impellers so that the forces acting thereupon will produce a resultant force opposite in direction and of a magnitude substantially equal to the total unbalanced forces acting upon the other portions of said shaft and impellers.

9. A multi-stage centrifugal pump including a casing, a shaft rotatably mounted therein, groups of single-suction type impellers mounted in opposed relation' upon said shaft and each impeller being adapted to form a close running fit with said casing, and means for balancing the end thrust of said impellers and shaft by proportioning the area of one of said running fits sufficiently different from the areas of the others of said running fits so that the forces acting thereupon will produce a resultant force opposite in direction and of a magnitude substantially equal to the total unbalanced ,forces acting upon the other portions of said shaft and impellers.

10. A multi-stage centrifugal pump including a casing, a shaft rotatably mounted therein, groups of single-suction type impellers mounted in opposed relation upon said shaft forming a unitary rotating structure, diaphragms between said impellers, said unitary structure arranged to form suitable close running fits with the diaphragm for eachstage of the pump, a fluid passage serially connectlng said impellers, and means tating structure by proportioning the area of one of said running fits suificiently difierent from the areas of the others of said rumiing fits so that the forces acting thereupon will produce a resultant force opposite in direction and of a magnitude substantially equal to the total unbalanced forces acting upon the other portions of said unitary rotating structure.

11. In a multi-stage centrifugal pump having impellers of single suction type disposed in groups opposed to each other upon a common shaft, there being unequal numbers ofaimpellers in the groups, diaphragms within said casing separating said impellers, and a spacing member between the adjacent impellers of the opposed groups and rotating therewith, the outside diameter of said member being greater than the diameters 125 'for balancing the end thrust of said unitary ro- 

